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[PATCH v20 6/6] Preserve visibility information of the concurrent data changes. 330+ messages / 2 participants [nested] [flat]
* [PATCH v20 6/6] Preserve visibility information of the concurrent data changes. @ 2025-08-30 17:40 Álvaro Herrera <alvherre@kurilemu.de> 0 siblings, 0 replies; 330+ messages in thread From: Álvaro Herrera @ 2025-08-30 17:40 UTC (permalink / raw) As explained in the commit message of the preceding patch of the series, the data changes done by applications while REPACK CONCURRENTLY is copying the table contents to a new file are decoded from WAL and eventually also applied to the new file. To reduce the complexity a little bit, the preceding patch uses the current transaction (i.e. transaction opened by the REPACK command) to execute those INSERT, UPDATE and DELETE commands. However, REPACK is not expected to change visibility of tuples. Therefore, this patch fixes the handling of the "concurrent data changes". It ensures that tuples written into the new table have the same XID and command ID (CID) as they had in the old table. To "replay" an UPDATE or DELETE command on the new table, we need the appropriate snapshot to find the previous tuple version in the new table. The (historic) snapshot we used to decode the UPDATE / DELETE should (by definition) see the state of the catalog prior to that UPDATE / DELETE. Thus we can use the same snapshot to find the "old tuple" for UPDATE / DELETE in the new table if: 1) REPACK CONCURRENTLY preserves visibility information of all tuples - that's the purpose of this part of the patch series. 2) The table being REPACKed is treated as a system catalog by all transactions that modify its data. This ensures that reorderbuffer.c generates a new snapshot for each data change in the table. We ensure 2) by maintaining a shared hashtable of tables being REPACKed CONCURRENTLY and by adjusting the RelationIsAccessibleInLogicalDecoding() macro so it checks this hashtable. (The corresponding flag is also added to the relation cache, so that the shared hashtable does not have to be accessed too often.) It's essential that after adding an entry to the hashtable we wait for completion of all the transactions that might have started to modify our table before our entry has was added. We achieve that by upgrading our lock on the table to ShareLock temporarily: as soon as we acquire it, no DML command should be running on the table. (This lock upgrade shouldn't cause any deadlock because we care to not hold a lock on other objects at the same time.) As long as we preserve the tuple visibility information (which includes XID), it's important to avoid logical decoding of the WAL generated by DMLs on the new table: the logical decoding subsystem probably does not expect that the incoming WAL records contain XIDs of an already decoded transactions. (And of course, repeated decoding would be wasted effort.) Author: Antonin Houska <ah@cybertec.at> Author: Mikhail Nikalayeu <mihailnikalayeu@gmail.com> (small changes) --- src/backend/access/common/toast_internals.c | 3 +- src/backend/access/heap/heapam.c | 51 ++- src/backend/access/heap/heapam_handler.c | 23 +- src/backend/access/transam/xact.c | 52 +++ src/backend/commands/cluster.c | 400 ++++++++++++++++-- src/backend/replication/logical/decode.c | 28 +- src/backend/replication/logical/snapbuild.c | 22 +- .../pgoutput_repack/pgoutput_repack.c | 68 ++- src/backend/storage/ipc/ipci.c | 2 + .../utils/activity/wait_event_names.txt | 1 + src/backend/utils/cache/inval.c | 21 + src/backend/utils/cache/relcache.c | 4 + src/include/access/heapam.h | 12 +- src/include/access/xact.h | 2 + src/include/commands/cluster.h | 22 + src/include/storage/lwlocklist.h | 1 + src/include/utils/inval.h | 2 + src/include/utils/rel.h | 7 +- src/include/utils/snapshot.h | 3 + .../injection_points/specs/repack.spec | 4 - src/tools/pgindent/typedefs.list | 1 + 21 files changed, 635 insertions(+), 94 deletions(-) diff --git a/src/backend/access/common/toast_internals.c b/src/backend/access/common/toast_internals.c index a1d0eed8953..586eb42a137 100644 --- a/src/backend/access/common/toast_internals.c +++ b/src/backend/access/common/toast_internals.c @@ -320,7 +320,8 @@ toast_save_datum(Relation rel, Datum value, memcpy(VARDATA(&chunk_data), data_p, chunk_size); toasttup = heap_form_tuple(toasttupDesc, t_values, t_isnull); - heap_insert(toastrel, toasttup, mycid, options, NULL); + heap_insert(toastrel, toasttup, GetCurrentTransactionId(), mycid, + options, NULL); /* * Create the index entry. We cheat a little here by not using diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index f9a4fe3faed..fd17286cabe 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -2070,7 +2070,7 @@ ReleaseBulkInsertStatePin(BulkInsertState bistate) /* * heap_insert - insert tuple into a heap * - * The new tuple is stamped with current transaction ID and the specified + * The new tuple is stamped with specified transaction ID and the specified * command ID. * * See table_tuple_insert for comments about most of the input flags, except @@ -2086,15 +2086,16 @@ ReleaseBulkInsertStatePin(BulkInsertState bistate) * reflected into *tup. */ void -heap_insert(Relation relation, HeapTuple tup, CommandId cid, - int options, BulkInsertState bistate) +heap_insert(Relation relation, HeapTuple tup, TransactionId xid, + CommandId cid, int options, BulkInsertState bistate) { - TransactionId xid = GetCurrentTransactionId(); HeapTuple heaptup; Buffer buffer; Buffer vmbuffer = InvalidBuffer; bool all_visible_cleared = false; + Assert(TransactionIdIsValid(xid)); + /* Cheap, simplistic check that the tuple matches the rel's rowtype. */ Assert(HeapTupleHeaderGetNatts(tup->t_data) <= RelationGetNumberOfAttributes(relation)); @@ -2176,8 +2177,15 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid, /* * If this is a catalog, we need to transmit combo CIDs to properly * decode, so log that as well. + * + * HEAP_INSERT_NO_LOGICAL should be set when applying data changes + * done by other transactions during REPACK CONCURRENTLY. In such a + * case, the insertion should not be decoded at all - see + * heap_decode(). (It's also set by raw_heap_insert() for TOAST, but + * TOAST does not pass this test anyway.) */ - if (RelationIsAccessibleInLogicalDecoding(relation)) + if ((options & HEAP_INSERT_NO_LOGICAL) == 0 && + RelationIsAccessibleInLogicalDecoding(relation)) log_heap_new_cid(relation, heaptup); /* @@ -2723,7 +2731,8 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples, void simple_heap_insert(Relation relation, HeapTuple tup) { - heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL); + heap_insert(relation, tup, GetCurrentTransactionId(), + GetCurrentCommandId(true), 0, NULL); } /* @@ -2780,11 +2789,11 @@ xmax_infomask_changed(uint16 new_infomask, uint16 old_infomask) */ TM_Result heap_delete(Relation relation, ItemPointer tid, - CommandId cid, Snapshot crosscheck, bool wait, - TM_FailureData *tmfd, bool changingPart, bool wal_logical) + TransactionId xid, CommandId cid, Snapshot crosscheck, bool wait, + TM_FailureData *tmfd, bool changingPart, + bool wal_logical) { TM_Result result; - TransactionId xid = GetCurrentTransactionId(); ItemId lp; HeapTupleData tp; Page page; @@ -2801,6 +2810,7 @@ heap_delete(Relation relation, ItemPointer tid, bool old_key_copied = false; Assert(ItemPointerIsValid(tid)); + Assert(TransactionIdIsValid(xid)); AssertHasSnapshotForToast(relation); @@ -3097,8 +3107,12 @@ l1: /* * For logical decode we need combo CIDs to properly decode the * catalog + * + * Like in heap_insert(), visibility is unchanged when called from + * VACUUM FULL / CLUSTER. */ - if (RelationIsAccessibleInLogicalDecoding(relation)) + if (wal_logical && + RelationIsAccessibleInLogicalDecoding(relation)) log_heap_new_cid(relation, &tp); xlrec.flags = 0; @@ -3217,11 +3231,12 @@ simple_heap_delete(Relation relation, ItemPointer tid) TM_Result result; TM_FailureData tmfd; - result = heap_delete(relation, tid, + result = heap_delete(relation, tid, GetCurrentTransactionId(), GetCurrentCommandId(true), InvalidSnapshot, true /* wait for commit */ , &tmfd, false, /* changingPart */ true /* wal_logical */ ); + switch (result) { case TM_SelfModified: @@ -3260,12 +3275,11 @@ simple_heap_delete(Relation relation, ItemPointer tid) */ TM_Result heap_update(Relation relation, ItemPointer otid, HeapTuple newtup, - CommandId cid, Snapshot crosscheck, bool wait, - TM_FailureData *tmfd, LockTupleMode *lockmode, + TransactionId xid, CommandId cid, Snapshot crosscheck, + bool wait, TM_FailureData *tmfd, LockTupleMode *lockmode, TU_UpdateIndexes *update_indexes, bool wal_logical) { TM_Result result; - TransactionId xid = GetCurrentTransactionId(); Bitmapset *hot_attrs; Bitmapset *sum_attrs; Bitmapset *key_attrs; @@ -3305,6 +3319,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup, infomask2_new_tuple; Assert(ItemPointerIsValid(otid)); + Assert(TransactionIdIsValid(xid)); /* Cheap, simplistic check that the tuple matches the rel's rowtype. */ Assert(HeapTupleHeaderGetNatts(newtup->t_data) <= @@ -4144,8 +4159,12 @@ l2: /* * For logical decoding we need combo CIDs to properly decode the * catalog. + * + * Like in heap_insert(), visibility is unchanged when called from + * VACUUM FULL / CLUSTER. */ - if (RelationIsAccessibleInLogicalDecoding(relation)) + if (wal_logical && + RelationIsAccessibleInLogicalDecoding(relation)) { log_heap_new_cid(relation, &oldtup); log_heap_new_cid(relation, heaptup); @@ -4511,7 +4530,7 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup, TM_FailureData tmfd; LockTupleMode lockmode; - result = heap_update(relation, otid, tup, + result = heap_update(relation, otid, tup, GetCurrentTransactionId(), GetCurrentCommandId(true), InvalidSnapshot, true /* wait for commit */ , &tmfd, &lockmode, update_indexes, diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c index d03084768e0..b50f7dc9b9c 100644 --- a/src/backend/access/heap/heapam_handler.c +++ b/src/backend/access/heap/heapam_handler.c @@ -253,7 +253,8 @@ heapam_tuple_insert(Relation relation, TupleTableSlot *slot, CommandId cid, tuple->t_tableOid = slot->tts_tableOid; /* Perform the insertion, and copy the resulting ItemPointer */ - heap_insert(relation, tuple, cid, options, bistate); + heap_insert(relation, tuple, GetCurrentTransactionId(), cid, options, + bistate); ItemPointerCopy(&tuple->t_self, &slot->tts_tid); if (shouldFree) @@ -276,7 +277,8 @@ heapam_tuple_insert_speculative(Relation relation, TupleTableSlot *slot, options |= HEAP_INSERT_SPECULATIVE; /* Perform the insertion, and copy the resulting ItemPointer */ - heap_insert(relation, tuple, cid, options, bistate); + heap_insert(relation, tuple, GetCurrentTransactionId(), cid, options, + bistate); ItemPointerCopy(&tuple->t_self, &slot->tts_tid); if (shouldFree) @@ -310,8 +312,8 @@ heapam_tuple_delete(Relation relation, ItemPointer tid, CommandId cid, * the storage itself is cleaning the dead tuples by itself, it is the * time to call the index tuple deletion also. */ - return heap_delete(relation, tid, cid, crosscheck, wait, tmfd, changingPart, - true); + return heap_delete(relation, tid, GetCurrentTransactionId(), cid, + crosscheck, wait, tmfd, changingPart, true); } @@ -329,7 +331,8 @@ heapam_tuple_update(Relation relation, ItemPointer otid, TupleTableSlot *slot, slot->tts_tableOid = RelationGetRelid(relation); tuple->t_tableOid = slot->tts_tableOid; - result = heap_update(relation, otid, tuple, cid, crosscheck, wait, + result = heap_update(relation, otid, tuple, GetCurrentTransactionId(), + cid, crosscheck, wait, tmfd, lockmode, update_indexes, true); ItemPointerCopy(&tuple->t_self, &slot->tts_tid); @@ -2477,9 +2480,15 @@ reform_and_rewrite_tuple(HeapTuple tuple, * flag to skip logical decoding: as soon as REPACK CONCURRENTLY swaps * the relation files, it drops this relation, so no logical * replication subscription should need the data. + * + * It is also crucial to stamp the new record with the exact same xid + * and cid, because the tuple must be visible to the snapshot of the + * applied concurrent change later. */ - heap_insert(NewHeap, copiedTuple, GetCurrentCommandId(true), - HEAP_INSERT_NO_LOGICAL, NULL); + CommandId cid = HeapTupleHeaderGetRawCommandId(tuple->t_data); + TransactionId xid = HeapTupleHeaderGetXmin(tuple->t_data); + + heap_insert(NewHeap, copiedTuple, xid, cid, HEAP_INSERT_NO_LOGICAL, NULL); } heap_freetuple(copiedTuple); diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c index 5670f2bfbde..e913594fc07 100644 --- a/src/backend/access/transam/xact.c +++ b/src/backend/access/transam/xact.c @@ -126,6 +126,18 @@ static FullTransactionId XactTopFullTransactionId = {InvalidTransactionId}; static int nParallelCurrentXids = 0; static TransactionId *ParallelCurrentXids; +/* + * Another case that requires TransactionIdIsCurrentTransactionId() to behave + * specially is when REPACK CONCURRENTLY is processing data changes made in + * the old storage of a table by other transactions. When applying the changes + * to the new storage, the backend executing the CLUSTER command needs to act + * on behalf on those other transactions. The transactions responsible for the + * changes in the old storage are stored in this array, sorted by + * xidComparator. + */ +static int nRepackCurrentXids = 0; +static TransactionId *RepackCurrentXids = NULL; + /* * Miscellaneous flag bits to record events which occur on the top level * transaction. These flags are only persisted in MyXactFlags and are intended @@ -973,6 +985,8 @@ TransactionIdIsCurrentTransactionId(TransactionId xid) int low, high; + Assert(nRepackCurrentXids == 0); + low = 0; high = nParallelCurrentXids - 1; while (low <= high) @@ -992,6 +1006,21 @@ TransactionIdIsCurrentTransactionId(TransactionId xid) return false; } + /* + * When executing CLUSTER CONCURRENTLY, the array of current transactions + * is given. + */ + if (nRepackCurrentXids > 0) + { + Assert(nParallelCurrentXids == 0); + + return bsearch(&xid, + RepackCurrentXids, + nRepackCurrentXids, + sizeof(TransactionId), + xidComparator) != NULL; + } + /* * We will return true for the Xid of the current subtransaction, any of * its subcommitted children, any of its parents, or any of their @@ -5661,6 +5690,29 @@ EndParallelWorkerTransaction(void) CurrentTransactionState->blockState = TBLOCK_DEFAULT; } +/* + * SetRepackCurrentXids + * Set the XID array that TransactionIdIsCurrentTransactionId() should + * use. + */ +void +SetRepackCurrentXids(TransactionId *xip, int xcnt) +{ + RepackCurrentXids = xip; + nRepackCurrentXids = xcnt; +} + +/* + * ResetRepackCurrentXids + * Undo the effect of SetRepackCurrentXids(). + */ +void +ResetRepackCurrentXids(void) +{ + RepackCurrentXids = NULL; + nRepackCurrentXids = 0; +} + /* * ShowTransactionState * Debug support diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c index 511b2bb6c43..a44724f3757 100644 --- a/src/backend/commands/cluster.c +++ b/src/backend/commands/cluster.c @@ -82,6 +82,11 @@ typedef struct * The following definitions are used for concurrent processing. */ +/* + * OID of the table being repacked by this backend. + */ +static Oid repacked_rel = InvalidOid; + /* * The locators are used to avoid logical decoding of data that we do not need * for our table. @@ -125,8 +130,10 @@ static List *get_tables_to_repack_partitioned(RepackCommand cmd, static bool cluster_is_permitted_for_relation(RepackCommand cmd, Oid relid, Oid userid); -static void begin_concurrent_repack(Relation rel); -static void end_concurrent_repack(void); +static void begin_concurrent_repack(Relation rel, Relation *index_p, + bool *entered_p); +static void end_concurrent_repack(bool error); +static void cluster_before_shmem_exit_callback(int code, Datum arg); static LogicalDecodingContext *setup_logical_decoding(Oid relid, const char *slotname, TupleDesc tupdesc); @@ -146,6 +153,7 @@ static void apply_concurrent_delete(Relation rel, HeapTuple tup_target, ConcurrentChange *change); static HeapTuple find_target_tuple(Relation rel, ScanKey key, int nkeys, HeapTuple tup_key, + Snapshot snapshot, IndexInsertState *iistate, TupleTableSlot *ident_slot, IndexScanDesc *scan_p); @@ -450,6 +458,8 @@ cluster_rel(RepackCommand cmd, bool usingindex, bool verbose = ((params->options & CLUOPT_VERBOSE) != 0); bool recheck = ((params->options & CLUOPT_RECHECK) != 0); bool concurrent = ((params->options & CLUOPT_CONCURRENT) != 0); + bool entered, + success; /* * Check that the correct lock is held. The lock mode is @@ -620,23 +630,30 @@ cluster_rel(RepackCommand cmd, bool usingindex, TransferPredicateLocksToHeapRelation(OldHeap); /* rebuild_relation does all the dirty work */ + entered = false; + success = false; PG_TRY(); { /* - * For concurrent processing, make sure that our logical decoding - * ignores data changes of other tables than the one we are - * processing. + * For concurrent processing, make sure that + * + * 1) our logical decoding ignores data changes of other tables than + * the one we are processing. + * + * 2) other transactions treat this table as if it was a system / user + * catalog, and WAL the relevant additional information. */ if (concurrent) - begin_concurrent_repack(OldHeap); + begin_concurrent_repack(OldHeap, &index, &entered); rebuild_relation(cmd, usingindex, OldHeap, index, save_userid, verbose, concurrent); + success = true; } PG_FINALLY(); { - if (concurrent) - end_concurrent_repack(); + if (concurrent && entered) + end_concurrent_repack(!success); } PG_END_TRY(); @@ -2396,6 +2413,47 @@ determine_clustered_index(Relation rel, bool usingindex, const char *indexname) } +/* + * Each relation being processed by REPACK CONCURRENTLY must be in the + * repackedRels hashtable. + */ +typedef struct RepackedRel +{ + Oid relid; + Oid dbid; +} RepackedRel; + +static HTAB *RepackedRelsHash = NULL; + +/* + * Maximum number of entries in the hashtable. + * + * A replication slot is needed for the processing, so use this GUC to + * allocate memory for the hashtable. + */ +#define MAX_REPACKED_RELS (max_replication_slots) + +Size +RepackShmemSize(void) +{ + return hash_estimate_size(MAX_REPACKED_RELS, sizeof(RepackedRel)); +} + +void +RepackShmemInit(void) +{ + HASHCTL info; + + info.keysize = sizeof(RepackedRel); + info.entrysize = info.keysize; + + RepackedRelsHash = ShmemInitHash("Repacked Relations", + MAX_REPACKED_RELS, + MAX_REPACKED_RELS, + &info, + HASH_ELEM | HASH_BLOBS); +} + /* * Call this function before REPACK CONCURRENTLY starts to setup logical * decoding. It makes sure that other users of the table put enough @@ -2410,11 +2468,119 @@ determine_clustered_index(Relation rel, bool usingindex, const char *indexname) * * Note that TOAST table needs no attention here as it's not scanned using * historic snapshot. + * + * 'index_p' is in/out argument because the function unlocks the index + * temporarily. + * + * 'enter_p' receives a bool value telling whether relation OID was entered + * into RepackedRelsHash or not. */ static void -begin_concurrent_repack(Relation rel) +begin_concurrent_repack(Relation rel, Relation *index_p, bool *entered_p) { - Oid toastrelid; + Oid relid, + toastrelid; + Relation index = NULL; + Oid indexid = InvalidOid; + RepackedRel key, + *entry; + bool found; + static bool before_shmem_exit_callback_setup = false; + + relid = RelationGetRelid(rel); + index = index_p ? *index_p : NULL; + + /* + * Make sure that we do not leave an entry in RepackedRelsHash if exiting + * due to FATAL. + */ + if (!before_shmem_exit_callback_setup) + { + before_shmem_exit(cluster_before_shmem_exit_callback, 0); + before_shmem_exit_callback_setup = true; + } + + memset(&key, 0, sizeof(key)); + key.relid = relid; + key.dbid = MyDatabaseId; + + *entered_p = false; + LWLockAcquire(RepackedRelsLock, LW_EXCLUSIVE); + entry = (RepackedRel *) + hash_search(RepackedRelsHash, &key, HASH_ENTER_NULL, &found); + if (found) + { + /* + * Since REPACK CONCURRENTLY takes ShareRowExclusiveLock, a conflict + * should occur much earlier. However that lock may be released + * temporarily, see below. Anyway, we should complain whatever the + * reason of the conflict might be. + */ + ereport(ERROR, + (errmsg("relation \"%s\" is already being processed by REPACK CONCURRENTLY", + RelationGetRelationName(rel)))); + } + if (entry == NULL) + ereport(ERROR, + (errmsg("too many requests for REPACK CONCURRENTLY at a time")), + (errhint("Please consider increasing the \"max_replication_slots\" configuration parameter."))); + + /* + * Even if anything fails below, the caller has to do cleanup in the + * shared memory. + */ + *entered_p = true; + + /* + * Enable the callback to remove the entry in case of exit. We should not + * do this earlier, otherwise an attempt to insert already existing entry + * could make us remove that entry (inserted by another backend) during + * ERROR handling. + */ + Assert(!OidIsValid(repacked_rel)); + repacked_rel = relid; + + LWLockRelease(RepackedRelsLock); + + /* + * Make sure that other backends are aware of the new hash entry as soon + * as they open our table. + */ + CacheInvalidateRelcacheImmediate(relid); + + /* + * Also make sure that the existing users of the table update their + * relcache entry as soon as they try to run DML commands on it. + * + * ShareLock is the weakest lock that conflicts with DMLs. If any backend + * has a lower lock, we assume it'll accept our invalidation message when + * it changes the lock mode. + * + * Before upgrading the lock on the relation, close the index temporarily + * to avoid a deadlock if another backend running DML already has its lock + * (ShareLock) on the table and waits for the lock on the index. + */ + if (index) + { + indexid = RelationGetRelid(index); + index_close(index, ShareUpdateExclusiveLock); + } + LockRelationOid(relid, ShareLock); + UnlockRelationOid(relid, ShareLock); + if (OidIsValid(indexid)) + { + /* + * Re-open the index and check that it hasn't changed while unlocked. + */ + check_index_is_clusterable(rel, indexid, ShareUpdateExclusiveLock); + + /* + * Return the new relcache entry to the caller. (It's been locked by + * the call above.) + */ + index = index_open(indexid, NoLock); + *index_p = index; + } /* Avoid logical decoding of other relations by this backend. */ repacked_rel_locator = rel->rd_locator; @@ -2432,15 +2598,122 @@ begin_concurrent_repack(Relation rel) /* * Call this when done with REPACK CONCURRENTLY. + * + * 'error' tells whether the function is being called in order to handle + * error. */ static void -end_concurrent_repack(void) +end_concurrent_repack(bool error) { + RepackedRel key; + RepackedRel *entry = NULL; + Oid relid = repacked_rel; + + /* Remove the relation from the hash if we managed to insert one. */ + if (OidIsValid(repacked_rel)) + { + memset(&key, 0, sizeof(key)); + key.relid = repacked_rel; + key.dbid = MyDatabaseId; + LWLockAcquire(RepackedRelsLock, LW_EXCLUSIVE); + entry = hash_search(RepackedRelsHash, &key, HASH_REMOVE, NULL); + LWLockRelease(RepackedRelsLock); + + /* + * Make others refresh their information whether they should still + * treat the table as catalog from the perspective of writing WAL. + * + * XXX Unlike entering the entry into the hashtable, we do not bother + * with locking and unlocking the table here: + * + * 1) On normal completion (and sometimes even on ERROR), the caller + * is already holding AccessExclusiveLock on the table, so there + * should be no relcache reference unaware of this change. + * + * 2) In the other cases, the worst scenario is that the other + * backends will write unnecessary information to WAL until they close + * the relation. + * + * Should we use ShareLock mode to fix 2) at least for the non-FATAL + * errors? (Our before_shmem_exit callback is in charge of FATAL, and + * that probably should not try to acquire any lock.) + */ + CacheInvalidateRelcacheImmediate(repacked_rel); + + /* + * By clearing this variable we also disable + * cluster_before_shmem_exit_callback(). + */ + repacked_rel = InvalidOid; + } + /* * Restore normal function of (future) logical decoding for this backend. */ repacked_rel_locator.relNumber = InvalidOid; repacked_rel_toast_locator.relNumber = InvalidOid; + + /* + * On normal completion (!error), we should not really fail to remove the + * entry. But if it wasn't there for any reason, raise ERROR to make sure + * the transaction is aborted: if other transactions, while changing the + * contents of the relation, didn't know that REPACK CONCURRENTLY was in + * progress, they could have missed to WAL enough information, and thus we + * could have produced an inconsistent table contents. + * + * On the other hand, if we are already handling an error, there's no + * reason to worry about inconsistent contents of the new storage because + * the transaction is going to be rolled back anyway. Furthermore, by + * raising ERROR here we'd shadow the original error. + */ + if (!error) + { + char *relname; + + if (OidIsValid(relid) && entry == NULL) + { + relname = get_rel_name(relid); + if (!relname) + ereport(ERROR, + (errmsg("cache lookup failed for relation %u", + relid))); + + ereport(ERROR, + (errmsg("relation \"%s\" not found among repacked relations", + relname))); + } + } +} + +/* + * A wrapper to call end_concurrent_repack() as a before_shmem_exit callback. + */ +static void +cluster_before_shmem_exit_callback(int code, Datum arg) +{ + if (OidIsValid(repacked_rel)) + end_concurrent_repack(true); +} + +/* + * Check if relation is currently being processed by REPACK CONCURRENTLY. + */ +bool +is_concurrent_repack_in_progress(Oid relid) +{ + RepackedRel key, + *entry; + + memset(&key, 0, sizeof(key)); + key.relid = relid; + key.dbid = MyDatabaseId; + + LWLockAcquire(RepackedRelsLock, LW_SHARED); + entry = (RepackedRel *) + hash_search(RepackedRelsHash, &key, HASH_FIND, NULL); + LWLockRelease(RepackedRelsLock); + + return entry != NULL; } /* @@ -2502,6 +2775,9 @@ setup_logical_decoding(Oid relid, const char *slotname, TupleDesc tupdesc) dstate->relid = relid; dstate->tstore = tuplestore_begin_heap(false, false, maintenance_work_mem); +#ifdef USE_ASSERT_CHECKING + dstate->last_change_xid = InvalidTransactionId; +#endif dstate->tupdesc = tupdesc; @@ -2649,6 +2925,7 @@ apply_concurrent_changes(RepackDecodingState *dstate, Relation rel, char *change_raw, *src; ConcurrentChange change; + Snapshot snapshot; bool isnull[1]; Datum values[1]; @@ -2717,8 +2994,30 @@ apply_concurrent_changes(RepackDecodingState *dstate, Relation rel, /* * Find the tuple to be updated or deleted. + * + * As the table being REPACKed concurrently is treated like a + * catalog, new CID is WAL-logged and decoded. And since we use + * the same XID that the original DMLs did, the snapshot used for + * the logical decoding (by now converted to a non-historic MVCC + * snapshot) should see the tuples inserted previously into the + * new heap and/or updated there. */ - tup_exist = find_target_tuple(rel, key, nkeys, tup_key, + snapshot = change.snapshot; + + /* + * Set what should be considered current transaction (and + * subtransactions) during visibility check. + * + * Note that this snapshot was created from a historic snapshot + * using SnapBuildMVCCFromHistoric(), which does not touch + * 'subxip'. Thus, unlike in a regular MVCC snapshot, the array + * only contains the transactions whose data changes we are + * applying, and its subtransactions. That's exactly what we need + * to check if particular xact is a "current transaction:". + */ + SetRepackCurrentXids(snapshot->subxip, snapshot->subxcnt); + + tup_exist = find_target_tuple(rel, key, nkeys, tup_key, snapshot, iistate, ident_slot, &ind_scan); if (tup_exist == NULL) elog(ERROR, "Failed to find target tuple"); @@ -2729,6 +3028,8 @@ apply_concurrent_changes(RepackDecodingState *dstate, Relation rel, else apply_concurrent_delete(rel, tup_exist, &change); + ResetRepackCurrentXids(); + if (tup_old != NULL) { pfree(tup_old); @@ -2741,14 +3042,14 @@ apply_concurrent_changes(RepackDecodingState *dstate, Relation rel, else elog(ERROR, "Unrecognized kind of change: %d", change.kind); - /* - * If a change was applied now, increment CID for next writes and - * update the snapshot so it sees the changes we've applied so far. - */ - if (change.kind != CHANGE_UPDATE_OLD) + /* Free the snapshot if this is the last change that needed it. */ + Assert(change.snapshot->active_count > 0); + change.snapshot->active_count--; + if (change.snapshot->active_count == 0) { - CommandCounterIncrement(); - UpdateActiveSnapshotCommandId(); + if (change.snapshot == dstate->snapshot) + dstate->snapshot = NULL; + FreeSnapshot(change.snapshot); } /* TTSOpsMinimalTuple has .get_heap_tuple==NULL. */ @@ -2768,16 +3069,35 @@ static void apply_concurrent_insert(Relation rel, ConcurrentChange *change, HeapTuple tup, IndexInsertState *iistate, TupleTableSlot *index_slot) { + Snapshot snapshot = change->snapshot; List *recheck; + /* + * For INSERT, the visibility information is not important, but we use the + * snapshot to get CID. Index functions might need the whole snapshot + * anyway. + */ + SetRepackCurrentXids(snapshot->subxip, snapshot->subxcnt); + + /* + * Write the tuple into the new heap. + * + * The snapshot is the one we used to decode the insert (though converted + * to "non-historic" MVCC snapshot), i.e. the snapshot's curcid is the + * tuple CID incremented by one (due to the "new CID" WAL record that got + * written along with the INSERT record). Thus if we want to use the + * original CID, we need to subtract 1 from curcid. + */ + Assert(snapshot->curcid != InvalidCommandId && + snapshot->curcid > FirstCommandId); /* * Like simple_heap_insert(), but make sure that the INSERT is not * logically decoded - see reform_and_rewrite_tuple() for more * information. */ - heap_insert(rel, tup, GetCurrentCommandId(true), HEAP_INSERT_NO_LOGICAL, - NULL); + heap_insert(rel, tup, change->xid, snapshot->curcid - 1, + HEAP_INSERT_NO_LOGICAL, NULL); /* * Update indexes. @@ -2785,6 +3105,7 @@ apply_concurrent_insert(Relation rel, ConcurrentChange *change, HeapTuple tup, * In case functions in the index need the active snapshot and caller * hasn't set one. */ + PushActiveSnapshot(snapshot); ExecStoreHeapTuple(tup, index_slot, false); recheck = ExecInsertIndexTuples(iistate->rri, index_slot, @@ -2795,6 +3116,8 @@ apply_concurrent_insert(Relation rel, ConcurrentChange *change, HeapTuple tup, NIL, /* arbiterIndexes */ false /* onlySummarizing */ ); + PopActiveSnapshot(); + ResetRepackCurrentXids(); /* * If recheck is required, it must have been preformed on the source @@ -2816,6 +3139,7 @@ apply_concurrent_update(Relation rel, HeapTuple tup, HeapTuple tup_target, TU_UpdateIndexes update_indexes; TM_Result res; List *recheck; + Snapshot snapshot = change->snapshot; /* * Write the new tuple into the new heap. ('tup' gets the TID assigned @@ -2823,13 +3147,19 @@ apply_concurrent_update(Relation rel, HeapTuple tup, HeapTuple tup_target, * * Do it like in simple_heap_update(), except for 'wal_logical' (and * except for 'wait'). + * + * Regarding CID, see the comment in apply_concurrent_insert(). */ + Assert(snapshot->curcid != InvalidCommandId && + snapshot->curcid > FirstCommandId); + res = heap_update(rel, &tup_target->t_self, tup, - GetCurrentCommandId(true), + change->xid, snapshot->curcid - 1, InvalidSnapshot, false, /* no wait - only we are doing changes */ &tmfd, &lockmode, &update_indexes, - false /* wal_logical */ ); + /* wal_logical */ + false); if (res != TM_Ok) ereport(ERROR, (errmsg("failed to apply concurrent UPDATE"))); @@ -2837,6 +3167,7 @@ apply_concurrent_update(Relation rel, HeapTuple tup, HeapTuple tup_target, if (update_indexes != TU_None) { + PushActiveSnapshot(snapshot); recheck = ExecInsertIndexTuples(iistate->rri, index_slot, iistate->estate, @@ -2846,6 +3177,7 @@ apply_concurrent_update(Relation rel, HeapTuple tup, HeapTuple tup_target, NIL, /* arbiterIndexes */ /* onlySummarizing */ update_indexes == TU_Summarizing); + PopActiveSnapshot(); list_free(recheck); } @@ -2858,6 +3190,12 @@ apply_concurrent_delete(Relation rel, HeapTuple tup_target, { TM_Result res; TM_FailureData tmfd; + Snapshot snapshot = change->snapshot; + + + /* Regarding CID, see the comment in apply_concurrent_insert(). */ + Assert(snapshot->curcid != InvalidCommandId && + snapshot->curcid > FirstCommandId); /* * Delete tuple from the new heap. @@ -2865,11 +3203,11 @@ apply_concurrent_delete(Relation rel, HeapTuple tup_target, * Do it like in simple_heap_delete(), except for 'wal_logical' (and * except for 'wait'). */ - res = heap_delete(rel, &tup_target->t_self, GetCurrentCommandId(true), - InvalidSnapshot, false, - &tmfd, - false, /* no wait - only we are doing changes */ - false /* wal_logical */ ); + res = heap_delete(rel, &tup_target->t_self, change->xid, + snapshot->curcid - 1, InvalidSnapshot, false, + &tmfd, false, + /* wal_logical */ + false); if (res != TM_Ok) ereport(ERROR, (errmsg("failed to apply concurrent DELETE"))); @@ -2890,7 +3228,7 @@ apply_concurrent_delete(Relation rel, HeapTuple tup_target, */ static HeapTuple find_target_tuple(Relation rel, ScanKey key, int nkeys, HeapTuple tup_key, - IndexInsertState *iistate, + Snapshot snapshot, IndexInsertState *iistate, TupleTableSlot *ident_slot, IndexScanDesc *scan_p) { IndexScanDesc scan; @@ -2899,7 +3237,7 @@ find_target_tuple(Relation rel, ScanKey key, int nkeys, HeapTuple tup_key, HeapTuple result = NULL; /* XXX no instrumentation for now */ - scan = index_beginscan(rel, iistate->ident_index, GetActiveSnapshot(), + scan = index_beginscan(rel, iistate->ident_index, snapshot, NULL, nkeys, 0); *scan_p = scan; index_rescan(scan, key, nkeys, NULL, 0); @@ -2971,6 +3309,8 @@ process_concurrent_changes(LogicalDecodingContext *ctx, XLogRecPtr end_of_wal, } PG_FINALLY(); { + ResetRepackCurrentXids(); + if (rel_src) rel_dst->rd_toastoid = InvalidOid; } diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c index 5dc4ae58ffe..9fefcffd8b3 100644 --- a/src/backend/replication/logical/decode.c +++ b/src/backend/replication/logical/decode.c @@ -475,9 +475,14 @@ heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf) /* * If the change is not intended for logical decoding, do not even - * establish transaction for it - REPACK CONCURRENTLY is the typical use - * case. - * + * establish transaction for it. This is particularly important if the + * record was generated by REPACK CONCURRENTLY because this command uses + * the original XID when doing changes in the new storage. The decoding + * system probably does not expect to see the same transaction multiple + * times. + */ + + /* * First, check if REPACK CONCURRENTLY is being performed by this backend. * If so, only decode data changes of the table that it is processing, and * the changes of its TOAST relation. @@ -504,11 +509,11 @@ heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf) * Second, skip records which do not contain sufficient information for * the decoding. * - * The problem we solve here is that REPACK CONCURRENTLY generates WAL - * when doing changes in the new table. Those changes should not be useful - * for any other user (such as logical replication subscription) because - * the new table will eventually be dropped (after REPACK CONCURRENTLY has - * assigned its file to the "old table"). + * One particular problem we solve here is that REPACK CONCURRENTLY + * generates WAL when doing changes in the new table. Those changes should + * not be decoded because reorderbuffer.c considers their XID already + * committed. (REPACK CONCURRENTLY deliberately generates WAL records in + * such a way that they are skipped here.) */ switch (info) { @@ -995,13 +1000,6 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf) xlrec = (xl_heap_insert *) XLogRecGetData(r); - /* - * Ignore insert records without new tuples (this does happen when - * raw_heap_insert marks the TOAST record as HEAP_INSERT_NO_LOGICAL). - */ - if (!(xlrec->flags & XLH_INSERT_CONTAINS_NEW_TUPLE)) - return; - /* only interested in our database */ XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL); if (target_locator.dbOid != ctx->slot->data.database) diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c index 8e5116a9cab..72a38074a7b 100644 --- a/src/backend/replication/logical/snapbuild.c +++ b/src/backend/replication/logical/snapbuild.c @@ -155,7 +155,7 @@ static bool ExportInProgress = false; static void SnapBuildPurgeOlderTxn(SnapBuild *builder); /* snapshot building/manipulation/distribution functions */ -static Snapshot SnapBuildBuildSnapshot(SnapBuild *builder); +static Snapshot SnapBuildBuildSnapshot(SnapBuild *builder, XLogRecPtr lsn); static void SnapBuildFreeSnapshot(Snapshot snap); @@ -352,12 +352,17 @@ SnapBuildSnapDecRefcount(Snapshot snap) * Build a new snapshot, based on currently committed catalog-modifying * transactions. * + * 'lsn' is the location of the commit record (of a catalog-changing + * transaction) that triggered creation of the snapshot. Pass + * InvalidXLogRecPtr for the transaction base snapshot or if it the user of + * the snapshot should not need the LSN. + * * In-progress transactions with catalog access are *not* allowed to modify * these snapshots; they have to copy them and fill in appropriate ->curcid * and ->subxip/subxcnt values. */ static Snapshot -SnapBuildBuildSnapshot(SnapBuild *builder) +SnapBuildBuildSnapshot(SnapBuild *builder, XLogRecPtr lsn) { Snapshot snapshot; Size ssize; @@ -425,6 +430,7 @@ SnapBuildBuildSnapshot(SnapBuild *builder) snapshot->active_count = 0; snapshot->regd_count = 0; snapshot->snapXactCompletionCount = 0; + snapshot->lsn = lsn; return snapshot; } @@ -461,7 +467,7 @@ SnapBuildInitialSnapshot(SnapBuild *builder) if (TransactionIdIsValid(MyProc->xmin)) elog(ERROR, "cannot build an initial slot snapshot when MyProc->xmin already is valid"); - snap = SnapBuildBuildSnapshot(builder); + snap = SnapBuildBuildSnapshot(builder, InvalidXLogRecPtr); /* * We know that snap->xmin is alive, enforced by the logical xmin @@ -502,7 +508,7 @@ SnapBuildInitialSnapshotForRepack(SnapBuild *builder) Assert(builder->state == SNAPBUILD_CONSISTENT); - snap = SnapBuildBuildSnapshot(builder); + snap = SnapBuildBuildSnapshot(builder, InvalidXLogRecPtr); return SnapBuildMVCCFromHistoric(snap, false); } @@ -636,7 +642,7 @@ SnapBuildGetOrBuildSnapshot(SnapBuild *builder) /* only build a new snapshot if we don't have a prebuilt one */ if (builder->snapshot == NULL) { - builder->snapshot = SnapBuildBuildSnapshot(builder); + builder->snapshot = SnapBuildBuildSnapshot(builder, InvalidXLogRecPtr); /* increase refcount for the snapshot builder */ SnapBuildSnapIncRefcount(builder->snapshot); } @@ -716,7 +722,7 @@ SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn) /* only build a new snapshot if we don't have a prebuilt one */ if (builder->snapshot == NULL) { - builder->snapshot = SnapBuildBuildSnapshot(builder); + builder->snapshot = SnapBuildBuildSnapshot(builder, lsn); /* increase refcount for the snapshot builder */ SnapBuildSnapIncRefcount(builder->snapshot); } @@ -1130,7 +1136,7 @@ SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid, if (builder->snapshot) SnapBuildSnapDecRefcount(builder->snapshot); - builder->snapshot = SnapBuildBuildSnapshot(builder); + builder->snapshot = SnapBuildBuildSnapshot(builder, lsn); /* we might need to execute invalidations, add snapshot */ if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, xid)) @@ -1958,7 +1964,7 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn) { SnapBuildSnapDecRefcount(builder->snapshot); } - builder->snapshot = SnapBuildBuildSnapshot(builder); + builder->snapshot = SnapBuildBuildSnapshot(builder, InvalidXLogRecPtr); SnapBuildSnapIncRefcount(builder->snapshot); ReorderBufferSetRestartPoint(builder->reorder, lsn); diff --git a/src/backend/replication/pgoutput_repack/pgoutput_repack.c b/src/backend/replication/pgoutput_repack/pgoutput_repack.c index 687fbbc59bb..28bd16f9cc7 100644 --- a/src/backend/replication/pgoutput_repack/pgoutput_repack.c +++ b/src/backend/replication/pgoutput_repack/pgoutput_repack.c @@ -32,7 +32,8 @@ static void plugin_truncate(struct LogicalDecodingContext *ctx, Relation relations[], ReorderBufferChange *change); static void store_change(LogicalDecodingContext *ctx, - ConcurrentChangeKind kind, HeapTuple tuple); + ConcurrentChangeKind kind, HeapTuple tuple, + TransactionId xid); void _PG_output_plugin_init(OutputPluginCallbacks *cb) @@ -100,6 +101,7 @@ plugin_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn, Relation relation, ReorderBufferChange *change) { RepackDecodingState *dstate; + Snapshot snapshot; dstate = (RepackDecodingState *) ctx->output_writer_private; @@ -107,6 +109,48 @@ plugin_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn, if (relation->rd_id != dstate->relid) return; + /* + * Catalog snapshot is fine because the table we are processing is + * temporarily considered a user catalog table. + */ + snapshot = GetCatalogSnapshot(InvalidOid); + Assert(snapshot->snapshot_type == SNAPSHOT_HISTORIC_MVCC); + Assert(!snapshot->suboverflowed); + + /* + * This should not happen, but if we don't have enough information to + * apply a new snapshot, the consequences would be bad. Thus prefer ERROR + * to Assert(). + */ + if (XLogRecPtrIsInvalid(snapshot->lsn)) + ereport(ERROR, (errmsg("snapshot has invalid LSN"))); + + /* + * reorderbuffer.c changes the catalog snapshot as soon as it sees a new + * CID or a commit record of a catalog-changing transaction. + */ + if (dstate->snapshot == NULL || snapshot->lsn != dstate->snapshot_lsn || + snapshot->curcid != dstate->snapshot->curcid) + { + /* CID should not go backwards. */ + Assert(dstate->snapshot == NULL || + snapshot->curcid >= dstate->snapshot->curcid || + change->txn->xid != dstate->last_change_xid); + + /* + * XXX Is it a problem that the copy is created in + * TopTransactionContext? + * + * XXX Wouldn't it be o.k. for SnapBuildMVCCFromHistoric() to set xcnt + * to 0 instead of converting xip in this case? The point is that + * transactions which are still in progress from the perspective of + * reorderbuffer.c could not be replayed yet, so we do not need to + * examine their XIDs. + */ + dstate->snapshot = SnapBuildMVCCFromHistoric(snapshot, false); + dstate->snapshot_lsn = snapshot->lsn; + } + /* Decode entry depending on its type */ switch (change->action) { @@ -124,7 +168,7 @@ plugin_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn, if (newtuple == NULL) elog(ERROR, "Incomplete insert info."); - store_change(ctx, CHANGE_INSERT, newtuple); + store_change(ctx, CHANGE_INSERT, newtuple, change->txn->xid); } break; case REORDER_BUFFER_CHANGE_UPDATE: @@ -141,9 +185,11 @@ plugin_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn, elog(ERROR, "Incomplete update info."); if (oldtuple != NULL) - store_change(ctx, CHANGE_UPDATE_OLD, oldtuple); + store_change(ctx, CHANGE_UPDATE_OLD, oldtuple, + change->txn->xid); - store_change(ctx, CHANGE_UPDATE_NEW, newtuple); + store_change(ctx, CHANGE_UPDATE_NEW, newtuple, + change->txn->xid); } break; case REORDER_BUFFER_CHANGE_DELETE: @@ -156,7 +202,7 @@ plugin_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn, if (oldtuple == NULL) elog(ERROR, "Incomplete delete info."); - store_change(ctx, CHANGE_DELETE, oldtuple); + store_change(ctx, CHANGE_DELETE, oldtuple, change->txn->xid); } break; default: @@ -190,13 +236,13 @@ plugin_truncate(struct LogicalDecodingContext *ctx, ReorderBufferTXN *txn, if (i == nrelations) return; - store_change(ctx, CHANGE_TRUNCATE, NULL); + store_change(ctx, CHANGE_TRUNCATE, NULL, InvalidTransactionId); } /* Store concurrent data change. */ static void store_change(LogicalDecodingContext *ctx, ConcurrentChangeKind kind, - HeapTuple tuple) + HeapTuple tuple, TransactionId xid) { RepackDecodingState *dstate; char *change_raw; @@ -266,6 +312,11 @@ store_change(LogicalDecodingContext *ctx, ConcurrentChangeKind kind, dst = dst_start + SizeOfConcurrentChange; memcpy(dst, tuple->t_data, tuple->t_len); + /* Initialize the other fields. */ + change.xid = xid; + change.snapshot = dstate->snapshot; + dstate->snapshot->active_count++; + /* The data has been copied. */ if (flattened) pfree(tuple); @@ -279,6 +330,9 @@ store: isnull[0] = false; tuplestore_putvalues(dstate->tstore, dstate->tupdesc_change, values, isnull); +#ifdef USE_ASSERT_CHECKING + dstate->last_change_xid = xid; +#endif /* Accounting. */ dstate->nchanges++; diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c index e9ddf39500c..e24e1795aa9 100644 --- a/src/backend/storage/ipc/ipci.c +++ b/src/backend/storage/ipc/ipci.c @@ -151,6 +151,7 @@ CalculateShmemSize(int *num_semaphores) size = add_size(size, InjectionPointShmemSize()); size = add_size(size, SlotSyncShmemSize()); size = add_size(size, AioShmemSize()); + size = add_size(size, RepackShmemSize()); /* include additional requested shmem from preload libraries */ size = add_size(size, total_addin_request); @@ -344,6 +345,7 @@ CreateOrAttachShmemStructs(void) WaitEventCustomShmemInit(); InjectionPointShmemInit(); AioShmemInit(); + RepackShmemInit(); } /* diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt index 5427da5bc1b..e94c83726d6 100644 --- a/src/backend/utils/activity/wait_event_names.txt +++ b/src/backend/utils/activity/wait_event_names.txt @@ -352,6 +352,7 @@ DSMRegistry "Waiting to read or update the dynamic shared memory registry." InjectionPoint "Waiting to read or update information related to injection points." SerialControl "Waiting to read or update shared <filename>pg_serial</filename> state." AioWorkerSubmissionQueue "Waiting to access AIO worker submission queue." +RepackedRels "Waiting to access to hash table with list of repacked relations." # # END OF PREDEFINED LWLOCKS (DO NOT CHANGE THIS LINE) diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c index 02505c88b8e..ecaa2283c2a 100644 --- a/src/backend/utils/cache/inval.c +++ b/src/backend/utils/cache/inval.c @@ -1643,6 +1643,27 @@ CacheInvalidateRelcache(Relation relation) databaseId, relationId); } +/* + * CacheInvalidateRelcacheImmediate + * Send invalidation message for the specified relation's relcache entry. + * + * Currently this is used in REPACK CONCURRENTLY, to make sure that other + * backends are aware that the command is being executed for the relation. + */ +void +CacheInvalidateRelcacheImmediate(Oid relid) +{ + SharedInvalidationMessage msg; + + msg.rc.id = SHAREDINVALRELCACHE_ID; + msg.rc.dbId = MyDatabaseId; + msg.rc.relId = relid; + /* check AddCatcacheInvalidationMessage() for an explanation */ + VALGRIND_MAKE_MEM_DEFINED(&msg, sizeof(msg)); + + SendSharedInvalidMessages(&msg, 1); +} + /* * CacheInvalidateRelcacheAll * Register invalidation of the whole relcache at the end of command. diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c index d27a4c30548..ea565b5b053 100644 --- a/src/backend/utils/cache/relcache.c +++ b/src/backend/utils/cache/relcache.c @@ -1279,6 +1279,10 @@ retry: /* make sure relation is marked as having no open file yet */ relation->rd_smgr = NULL; + /* Is REPACK CONCURRENTLY in progress? */ + relation->rd_repack_concurrent = + is_concurrent_repack_in_progress(targetRelId); + /* * now we can free the memory allocated for pg_class_tuple */ diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h index b82dd17a966..981425f23b6 100644 --- a/src/include/access/heapam.h +++ b/src/include/access/heapam.h @@ -316,22 +316,24 @@ extern BulkInsertState GetBulkInsertState(void); extern void FreeBulkInsertState(BulkInsertState); extern void ReleaseBulkInsertStatePin(BulkInsertState bistate); -extern void heap_insert(Relation relation, HeapTuple tup, CommandId cid, - int options, BulkInsertState bistate); +extern void heap_insert(Relation relation, HeapTuple tup, TransactionId xid, + CommandId cid, int options, BulkInsertState bistate); extern void heap_multi_insert(Relation relation, struct TupleTableSlot **slots, int ntuples, CommandId cid, int options, BulkInsertState bistate); extern TM_Result heap_delete(Relation relation, ItemPointer tid, - CommandId cid, Snapshot crosscheck, bool wait, + TransactionId xid, CommandId cid, + Snapshot crosscheck, bool wait, struct TM_FailureData *tmfd, bool changingPart, bool wal_logical); extern void heap_finish_speculative(Relation relation, ItemPointer tid); extern void heap_abort_speculative(Relation relation, ItemPointer tid); extern TM_Result heap_update(Relation relation, ItemPointer otid, - HeapTuple newtup, + HeapTuple newtup, TransactionId xid, CommandId cid, Snapshot crosscheck, bool wait, struct TM_FailureData *tmfd, LockTupleMode *lockmode, - TU_UpdateIndexes *update_indexes, bool wal_logical); + TU_UpdateIndexes *update_indexes, + bool wal_logical); extern TM_Result heap_lock_tuple(Relation relation, HeapTuple tuple, CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy, bool follow_updates, diff --git a/src/include/access/xact.h b/src/include/access/xact.h index b2bc10ee041..fbb66d559b6 100644 --- a/src/include/access/xact.h +++ b/src/include/access/xact.h @@ -482,6 +482,8 @@ extern Size EstimateTransactionStateSpace(void); extern void SerializeTransactionState(Size maxsize, char *start_address); extern void StartParallelWorkerTransaction(char *tstatespace); extern void EndParallelWorkerTransaction(void); +extern void SetRepackCurrentXids(TransactionId *xip, int xcnt); +extern void ResetRepackCurrentXids(void); extern bool IsTransactionBlock(void); extern bool IsTransactionOrTransactionBlock(void); extern char TransactionBlockStatusCode(void); diff --git a/src/include/commands/cluster.h b/src/include/commands/cluster.h index 4a508c57a50..5dba3d427f5 100644 --- a/src/include/commands/cluster.h +++ b/src/include/commands/cluster.h @@ -61,6 +61,14 @@ typedef struct ConcurrentChange /* See the enum above. */ ConcurrentChangeKind kind; + /* Transaction that changes the data. */ + TransactionId xid; + + /* + * Historic catalog snapshot that was used to decode this change. + */ + Snapshot snapshot; + /* * The actual tuple. * @@ -92,6 +100,8 @@ typedef struct RepackDecodingState * tuplestore does this transparently. */ Tuplestorestate *tstore; + /* XID of the last change added to tstore. */ + TransactionId last_change_xid PG_USED_FOR_ASSERTS_ONLY; /* The current number of changes in tstore. */ double nchanges; @@ -112,6 +122,14 @@ typedef struct RepackDecodingState /* Slot to retrieve data from tstore. */ TupleTableSlot *tsslot; + /* + * Historic catalog snapshot that was used to decode the most recent + * change. + */ + Snapshot snapshot; + /* LSN of the record */ + XLogRecPtr snapshot_lsn; + ResourceOwner resowner; } RepackDecodingState; @@ -141,4 +159,8 @@ extern void finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap, MultiXactId cutoffMulti, char newrelpersistence); +extern Size RepackShmemSize(void); +extern void RepackShmemInit(void); +extern bool is_concurrent_repack_in_progress(Oid relid); + #endif /* CLUSTER_H */ diff --git a/src/include/storage/lwlocklist.h b/src/include/storage/lwlocklist.h index 06a1ffd4b08..9a9880b3073 100644 --- a/src/include/storage/lwlocklist.h +++ b/src/include/storage/lwlocklist.h @@ -85,6 +85,7 @@ PG_LWLOCK(50, DSMRegistry) PG_LWLOCK(51, InjectionPoint) PG_LWLOCK(52, SerialControl) PG_LWLOCK(53, AioWorkerSubmissionQueue) +PG_LWLOCK(54, RepackedRels) /* * There also exist several built-in LWLock tranches. As with the predefined diff --git a/src/include/utils/inval.h b/src/include/utils/inval.h index 9b871caef62..ae9dee394dc 100644 --- a/src/include/utils/inval.h +++ b/src/include/utils/inval.h @@ -50,6 +50,8 @@ extern void CacheInvalidateCatalog(Oid catalogId); extern void CacheInvalidateRelcache(Relation relation); +extern void CacheInvalidateRelcacheImmediate(Oid relid); + extern void CacheInvalidateRelcacheAll(void); extern void CacheInvalidateRelcacheByTuple(HeapTuple classTuple); diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h index b552359915f..66de3bc0c29 100644 --- a/src/include/utils/rel.h +++ b/src/include/utils/rel.h @@ -253,6 +253,9 @@ typedef struct RelationData bool pgstat_enabled; /* should relation stats be counted */ /* use "struct" here to avoid needing to include pgstat.h: */ struct PgStat_TableStatus *pgstat_info; /* statistics collection area */ + + /* Is REPACK CONCURRENTLY being performed on this relation? */ + bool rd_repack_concurrent; } RelationData; @@ -695,7 +698,9 @@ RelationCloseSmgr(Relation relation) #define RelationIsAccessibleInLogicalDecoding(relation) \ (XLogLogicalInfoActive() && \ RelationNeedsWAL(relation) && \ - (IsCatalogRelation(relation) || RelationIsUsedAsCatalogTable(relation))) + (IsCatalogRelation(relation) || \ + RelationIsUsedAsCatalogTable(relation) || \ + (relation)->rd_repack_concurrent)) /* * RelationIsLogicallyLogged diff --git a/src/include/utils/snapshot.h b/src/include/utils/snapshot.h index 0e546ec1497..014f27db7d7 100644 --- a/src/include/utils/snapshot.h +++ b/src/include/utils/snapshot.h @@ -13,6 +13,7 @@ #ifndef SNAPSHOT_H #define SNAPSHOT_H +#include "access/xlogdefs.h" #include "lib/pairingheap.h" @@ -201,6 +202,8 @@ typedef struct SnapshotData uint32 regd_count; /* refcount on RegisteredSnapshots */ pairingheap_node ph_node; /* link in the RegisteredSnapshots heap */ + XLogRecPtr lsn; /* position in the WAL stream when taken */ + /* * The transaction completion count at the time GetSnapshotData() built * this snapshot. Allows to avoid re-computing static snapshots when no diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index 75850334986..3711a7c92b9 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -86,9 +86,6 @@ step change_new # When applying concurrent data changes, we should see the effects of an # in-progress subtransaction. # -# XXX Not sure this test is useful now - it was designed for the patch that -# preserves tuple visibility and which therefore modifies -# TransactionIdIsCurrentTransactionId(). step change_subxact1 { BEGIN; @@ -103,7 +100,6 @@ step change_subxact1 # When applying concurrent data changes, we should not see the effects of a # rolled back subtransaction. # -# XXX Is this test useful? See above. step change_subxact2 { BEGIN; diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index b64ab8dfab4..9f5f331cad6 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -2540,6 +2540,7 @@ ReorderBufferTupleCidKey ReorderBufferUpdateProgressTxnCB ReorderTuple RepOriginId +RepackedRel RepackCommand RepackDecodingState RepackStmt -- 2.39.5 --3q6txozlgl6t37td-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
* [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions @ 2026-05-23 14:09 Mats Kindahl <mats@kindahl.net> 0 siblings, 0 replies; 330+ messages in thread From: Mats Kindahl @ 2026-05-23 14:09 UTC (permalink / raw) Two PostgreSQL standbys can independently promote to the same timeline ID if their primary stopped before either had a chance to promote. In that situation both clusters share a timeline history prefix that looks identical to pg_rewind: same TLI numbers and same begin/end LSNs. The existing same-TLI shortcut therefore treated the source as a valid rewind target and skipped the rewind entirely, leaving the target's diverged WAL intact. Fix this by embedding a UUIDv7 value in every timeline history file entry at promotion time. Each promotion generates a fresh UUID, so two independent promotions to the same TLI will carry different UUIDs even though the TLI number and begin LSN are identical. When loading the timeline history, pg_rewind uses these UUIDs in two places: 1. findCommonAncestorTimeline checks that the TLI and UUID in each entry match. A mismatch signals independent promotions and the search continues to earlier entries to find the true common ancestor. 2. The same-TLI shortcut (source and target on the same current TLI) compares the UUID stored in the last completed history entry and a mismatch forces a full rewind instead of a no-op. UUIDs are zero for clusters that predate this change, and the comparison function treats a zero UUID on either side as different from a UUID since that promotion has to be from a different server (it had a pre-change version server that was promoted, so it cannot be the same as a post-change version server that was promoted). Two new tests in t/005_same_timeline.pl cover both detection paths. The first covers the same-TLI shortcut: two standbys independently promote to TLI2 and TLI2', each with a distinct UUID. The second covers the ancestor search: the target goes through TLI1 -> TLI2 -> TLI3 while the source independently promoted so that it has a timeline with TLI1 -> TLI2' -> TLI3'. The test ensures that findCommonAncestorTimeline backs up to TLI1 as the true common ancestor rather than accepting the numerically matching TLI2 entry. --- src/backend/access/transam/timeline.c | 77 ++++- src/backend/access/transam/xlog.c | 15 + src/backend/utils/adt/uuid.c | 15 +- src/bin/pg_rewind/pg_rewind.c | 104 ++++++- src/bin/pg_rewind/t/005_same_timeline.pl | 362 +++++++++++++++++++++++ src/bin/pg_rewind/timeline.c | 47 ++- src/include/access/timeline.h | 5 +- src/include/access/xlog_internal.h | 1 + src/include/utils/uuid.h | 10 +- 9 files changed, 614 insertions(+), 22 deletions(-) diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index d80c8ffe0a7..237511b7521 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -42,6 +42,8 @@ #include "pgstat.h" #include "storage/fd.h" #include "utils/wait_event.h" +#include "utils/fmgrprotos.h" +#include "utils/uuid.h" /* * Copies all timeline history files with id's between 'begin' and 'end' @@ -110,8 +112,12 @@ readTimeLineHistory(TimeLineID targetTLI) ereport(FATAL, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); - /* Not there, so assume no parents */ - entry = palloc_object(TimeLineHistoryEntry); + + /* + * Not there, so assume no parents. We use palloc0_object to ensure + * that tluuid is all-zero. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = entry->end = InvalidXLogRecPtr; return list_make1(entry); @@ -125,6 +131,7 @@ readTimeLineHistory(TimeLineID targetTLI) prevend = InvalidXLogRecPtr; for (;;) { + char uuid_str[UUID_STR_LEN + 1] = {0}; char fline[MAXPGPATH]; char *res; char *ptr; @@ -155,7 +162,8 @@ readTimeLineHistory(TimeLineID targetTLI) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = + sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -164,7 +172,7 @@ readTimeLineHistory(TimeLineID targetTLI) (errmsg("syntax error in history file: %s", fline), errhint("Expected a numeric timeline ID."))); } - if (nfields != 3) + if (nfields < 3) ereport(FATAL, (errmsg("syntax error in history file: %s", fline), errhint("Expected a write-ahead log switchpoint location."))); @@ -176,12 +184,45 @@ readTimeLineHistory(TimeLineID targetTLI) lasttli = tli; - entry = palloc_object(TimeLineHistoryEntry); + /* + * We use palloc0_object to ensure that tluuid is all-zero, which is + * important for pg_rewind to detect whether the history file is + * missing or not. + */ + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = tli; entry->begin = prevend; entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4. It is in theory possible that the reason string + * starts with a UUID, but the current usage do not store a UUID. This + * allows us to support both old and new formats of history files + * without breaking compatibility by checking if the field contains a + * valid UUID. + */ + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + { + PG_TRY(); + { + Datum datum = DirectFunctionCall1(uuid_in, CStringGetDatum(uuid_str)); + + memcpy(&entry->tluuid, DatumGetUUIDP(datum), sizeof(pg_uuid_t)); + } + PG_CATCH(); + { + ErrorData *edata = CopyErrorData(); + + FlushErrorState(); + ereport(FATAL, + errmsg("invalid UUID in history file \"%s\"", path), + errdetail("%s", edata->message)); + } + PG_END_TRY(); + } + /* Build list with newest item first */ result = lcons(entry, result); @@ -197,9 +238,11 @@ readTimeLineHistory(TimeLineID targetTLI) /* * Create one more entry for the "tip" of the timeline, which has no entry - * in the history file. + * in the history file. We use palloc0_object to ensure that tluuid is + * all-zero, which is important for pg_rewind to detect whether the + * history file is missing or not. */ - entry = palloc_object(TimeLineHistoryEntry); + entry = palloc0_object(TimeLineHistoryEntry); entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; @@ -294,21 +337,33 @@ findNewestTimeLine(TimeLineID startTLI) * * newTLI: ID of the new timeline * parentTLI: ID of its immediate parent + * newTLUUID: UUID uniquely identifying this promotion instance * switchpoint: WAL location where the system switched to the new timeline * reason: human-readable explanation of why the timeline was switched * + * The output file is named <newTLI>.history (e.g. 00000003.history). If two + * servers independently promote to the same timeline ID, their history files + * share the same name. In a shared WAL archive the second file to arrive + * silently overwrites the first. The newTLUUID written into the file content + * lets pg_rewind detect this collision: it fetches each server's history file + * directly from that server, compares the UUIDs for every shared TLI, and + * treats a UUID mismatch as evidence of independent promotion even when the + * TLI numbers agree. + * * Currently this is only used at the end recovery, and so there are no locking * considerations. But we should be just as tense as XLogFileInit to avoid * emplacing a bogus file. */ void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason) { char path[MAXPGPATH]; char tmppath[MAXPGPATH]; char histfname[MAXFNAMELEN]; char buffer[BLCKSZ]; + char *uuid_str; int srcfd; int fd; ssize_t nbytes; @@ -398,13 +453,19 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * * If we did have a parent file, insert an extra newline just in case the * parent file failed to end with one. + * + * Format: <parentTLI>\t<switchpoint>\t<ThisTimeLineUUID>\t<reason>\n */ + uuid_str = DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(newTLUUID))); + snprintf(buffer, sizeof(buffer), - "%s%u\t%X/%08X\t%s\n", + "%s%u\t%X/%08X\t%s\t%s\n", (srcfd < 0) ? "" : "\n", parentTLI, LSN_FORMAT_ARGS(switchpoint), + uuid_str, reason); + pfree(uuid_str); nbytes = strlen(buffer); errno = 0; diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..fde491bff5f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -99,6 +99,7 @@ #include "storage/subsystems.h" #include "storage/sync.h" #include "utils/guc_hooks.h" +#include "utils/uuid.h" #include "utils/guc_tables.h" #include "utils/injection_point.h" #include "utils/pgstat_internal.h" @@ -6376,6 +6377,9 @@ StartupXLOG(void) newTLI = endOfRecoveryInfo->lastRecTLI; if (ArchiveRecoveryRequested) { + struct timeval tv; + pg_uuid_t uuid_buf; + newTLI = findNewestTimeLine(recoveryTargetTLI) + 1; ereport(LOG, (errmsg("selected new timeline ID: %u", newTLI))); @@ -6406,8 +6410,19 @@ StartupXLOG(void) * to the new timeline, and will try to connect to the new timeline. * To minimize the window for that, try to do as little as possible * between here and writing the end-of-recovery record. + * + * Generate a UUIDv7 that uniquely identifies this promotion. The + * same UUID is written into the history file so that pg_rewind can + * distinguish two servers that independently promoted to the same + * timeline ID. Use gettimeofday() since we are not on a hot path; + * generate_uuidv7 wants milliseconds and we pass 0 for sub-ms since + * the random bits already distinguish UUIDs generated within the same + * millisecond. */ + gettimeofday(&tv, NULL); + generate_uuidv7_r(&uuid_buf, tv.tv_sec * 1000 + tv.tv_usec / 1000, 0); writeTimeLineHistory(newTLI, recoveryTargetTLI, + &uuid_buf, EndOfLog, endOfRecoveryInfo->recoveryStopReason); ereport(LOG, diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c index a9edceabab0..c153131e9f5 100644 --- a/src/backend/utils/adt/uuid.c +++ b/src/backend/utils/adt/uuid.c @@ -89,7 +89,7 @@ static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup); static Datum uuid_abbrev_convert(Datum original, SortSupport ssup); static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version); static inline int64 get_real_time_ns_ascending(void); -static pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); Datum uuid_in(PG_FUNCTION_ARGS) @@ -616,6 +616,14 @@ get_real_time_ns_ascending(void) return ns; } +pg_uuid_t * +generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +{ + pg_uuid_t *uuid = palloc(UUID_LEN); + + return generate_uuidv7_r(uuid, unix_ts_ms, sub_ms); +} + /* * Generate UUID version 7 per RFC 9562, with the given timestamp. * @@ -632,10 +640,9 @@ get_real_time_ns_ascending(void) * * NB: all numbers here are unsigned, unix_ts_ms cannot be negative per RFC. */ -static pg_uuid_t * -generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms) +pg_uuid_t * +generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms) { - pg_uuid_t *uuid = palloc(UUID_LEN); uint32 increased_clock_precision; /* Fill in time part */ diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 2e86fd158d0..ffb12b1ba4a 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -32,6 +32,19 @@ #include "rewind_source.h" #include "storage/bufpage.h" +/* + * Timeline histories for both clusters, populated by matchAndFetchTimelines(). + */ +typedef struct TimeLineHistoriesData +{ + TimeLineHistoryEntry *source, + *target; + int sourceNentries, + targetNentries; +} TimeLineHistoriesData; + +typedef TimeLineHistoriesData *TimeLineHistories; + static void usage(const char *progname); static void perform_rewind(filemap_t *filemap, rewind_source *source, @@ -53,6 +66,9 @@ static void findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, TimeLineHistoryEntry *b_history, int b_nentries, XLogRecPtr *recptr, int *tliIndex); +static inline bool matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b); +static bool matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, + TimeLineHistories timelineHistories); static void ensureCleanShutdown(const char *argv0); static void disconnect_atexit(void); @@ -141,6 +157,7 @@ main(int argc, char **argv) int c; XLogRecPtr divergerec; int lastcommontliIndex; + TimeLineHistoriesData timelineHistories; XLogRecPtr chkptrec; TimeLineID chkpttli; XLogRecPtr chkptredo; @@ -374,10 +391,21 @@ main(int argc, char **argv) * * If both clusters are already on the same timeline, there's nothing to * do. + * + * This also handles the case when two servers independently promoted to + * the same timeline ID: one crashed after writing the history file but + * before its EOR WAL record was distributed, so a second standby promoted + * independently. The history files produced by those two promotions + * carry different UUIDs. + * + * When the clusters are on different timelines we locate the fork point + * via findCommonAncestorTimeline. */ - if (target_tli == source_tli) + if (matchAndFetchTimelines(source_tli, target_tli, &timelineHistories)) { pg_log_info("source and target cluster are on the same timeline"); + pfree(timelineHistories.source); + pfree(timelineHistories.target); rewind_needed = false; target_wal_endrec = InvalidXLogRecPtr; } @@ -391,8 +419,10 @@ main(int argc, char **argv) * Retrieve timelines for both source and target, and find the point * where they diverged. */ - sourceHistory = getTimelineHistory(source_tli, true, &sourceNentries); - targetHistory = getTimelineHistory(target_tli, false, &targetNentries); + targetHistory = timelineHistories.target; + targetNentries = timelineHistories.targetNentries; + sourceHistory = timelineHistories.source; + sourceNentries = timelineHistories.sourceNentries; findCommonAncestorTimeline(sourceHistory, sourceNentries, targetHistory, targetNentries, @@ -876,7 +906,7 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) */ if (tli == 1) { - history = pg_malloc_object(TimeLineHistoryEntry); + history = pg_malloc0_object(TimeLineHistoryEntry); history->tli = tli; history->begin = history->end = InvalidXLogRecPtr; *nentries = 1; @@ -922,6 +952,56 @@ getTimelineHistory(TimeLineID tli, bool is_source, int *nentries) return history; } +/* + * Return true if two per-entry promotion UUIDs are compatible. + * + * A zero UUID means the history file predates this fix (or the entry is + * synthetic). If both sides are zero we have no UUID information and fall + * back to TLI-number-only matching (backward compatibility with old servers). + * If one side carries a UUID and the other does not, they cannot originate + * from the same promotion and are treated as incompatible. + */ +static inline bool +matchingTimelineUUID(TimeLineHistoryEntry *a, TimeLineHistoryEntry *b) +{ + static const pg_uuid_t zero = {{0}}; + + if (memcmp(&a->tluuid, &zero, UUID_LEN) == 0 && memcmp(&b->tluuid, &zero, UUID_LEN) == 0) + return true; + return memcmp(&a->tluuid, &b->tluuid, UUID_LEN) == 0; +} + +/* + * Fetch the timeline history for both clusters, store them in tlh, and return + * true if the clusters are on the same timeline (no rewind needed). + * + * tlh is always fully populated on return regardless of the result, so the + * caller can pass tlh->source / tlh->target directly to + * findCommonAncestorTimeline() when the return value is false. + * + * TLI 1 always returns true: it is the original timeline and has no promotion + * UUID. For TLI >= 2, the UUID in entry[Nentries - 2] identifies the + * promotion that created the current TLI. Both-zero UUIDs (old history files) + * are treated as compatible; zero-vs-nonzero is treated as a mismatch because + * one side carries a promotion UUID and they cannot be the same promotion. + */ +static bool +matchAndFetchTimelines(TimeLineID source_tli, TimeLineID target_tli, TimeLineHistories tlh) +{ + tlh->source = getTimelineHistory(source_tli, true, &tlh->sourceNentries); + tlh->target = getTimelineHistory(target_tli, false, &tlh->targetNentries); + + if (source_tli != target_tli) + return false; + + /* TLI 1 has no promotion UUID; always treat as the same timeline. */ + if (tlh->sourceNentries < 2 || tlh->targetNentries < 2) + return true; + + return matchingTimelineUUID(&tlh->source[tlh->sourceNentries - 2], + &tlh->target[tlh->targetNentries - 2]); +} + /* * Determine the TLI of the last common timeline in the timeline history of * two clusters. *tliIndex is set to the index of last common timeline in @@ -943,12 +1023,26 @@ findCommonAncestorTimeline(TimeLineHistoryEntry *a_history, int a_nentries, * depending on the history files that each node has fetched in previous * recovery processes. Hence check the start position of the new timeline * as well and move down by one extra timeline entry if they do not match. + * + * We also compare timeline UUIDs when both sides carry one. Two servers + * that independently promoted to the same timeline ID produce history + * files with the same name (e.g. 00000003.history); in a shared WAL + * archive the second file silently overwrites the first. pg_rewind + * fetches each server's history file directly from that server, so it + * sees both UUIDs. + * + * The timeline UUID stored in history entry[i] is the UUID of the + * promotion that created entry[i+1], i.e. the UUID of TLI entry[i+1].tli. + * So to check whether entry[i] itself represents the same timeline on + * both sides we look at entry[i-1].tluuid (for i > 0). TLI 1 (i == 0) is + * always the same: it is the original timeline and has no promotion UUID. */ n = Min(a_nentries, b_nentries); for (i = 0; i < n; i++) { if (a_history[i].tli != b_history[i].tli || - a_history[i].begin != b_history[i].begin) + a_history[i].begin != b_history[i].begin || + (i > 0 && !matchingTimelineUUID(&a_history[i - 1], &b_history[i - 1]))) break; } diff --git a/src/bin/pg_rewind/t/005_same_timeline.pl b/src/bin/pg_rewind/t/005_same_timeline.pl index 95a40c3b270..2360c3df1d0 100644 --- a/src/bin/pg_rewind/t/005_same_timeline.pl +++ b/src/bin/pg_rewind/t/005_same_timeline.pl @@ -7,6 +7,8 @@ # use strict; use warnings FATAL => 'all'; +use File::Copy; +use PostgreSQL::Test::Cluster; use PostgreSQL::Test::Utils; use Test::More; @@ -21,4 +23,364 @@ RewindTest::create_standby(); RewindTest::run_pg_rewind('local'); RewindTest::clean_rewind_test(); +# Helper function to run pg_rewind in local mode with the given source and +# target nodes and extra arguments. +# +# The target and source nodes are stopped before the call and the target is +# restarted afterward. The target's postgresql.conf is copied to a temporary +# location and passed to pg_rewind with --config-file, so that pg_rewind can +# update the target's config file in place without worrying about file +# permissions. The temporary config file is moved back to the target's data +# directory and permissions fixed after pg_rewind finishes. +sub rewind_node +{ + my ($target, $source, $label, @extra_args) = @_; + $source->stop; + $target->stop; + + my $tpgdata = $target->data_dir; + my $tmp = PostgreSQL::Test::Utils::tempdir; + copy("$tpgdata/postgresql.conf", "$tmp/target-postgresql.conf.tmp"); + + command_ok( + [ + 'pg_rewind', + '--debug', + '--source-pgdata' => $source->data_dir, + '--target-pgdata' => $target->data_dir, + '--no-sync', + '--config-file' => "$tmp/target-postgresql.conf.tmp", + @extra_args, + ], + $label); + + move("$tmp/target-postgresql.conf.tmp", "$tpgdata/postgresql.conf"); + chmod($target->group_access() ? 0640 : 0600, "$tpgdata/postgresql.conf") + or BAIL_OUT("unable to set permissions for $tpgdata/postgresql.conf"); + + $target->start; +} + +# Rewrite a node's TLI history file in the old 3-field format (no UUID), so +# that pg_rewind sees a zero UUID for that side, as if the node had been +# promoted by a server that predates the UUID feature. +sub strip_tli_uuid +{ + my ($node, $tli) = @_; + my $histfile = sprintf("%s/pg_wal/%08X.history", $node->data_dir, $tli); + open(my $fh, '<', $histfile) or die "cannot open $histfile: $!"; + my @lines = <$fh>; + close $fh; + open($fh, '>', $histfile) or die "cannot write $histfile: $!"; + for my $line (@lines) + { + chomp $line; + my @f = split(/\t/, $line, 4); + if (@f == 4) + { + # Drop the UUID field (index 2); keep parentTLI, switchpoint, reason. + print $fh join("\t", $f[0], $f[1], $f[3]) . "\n"; + } + else + { + print $fh "$line\n"; + } + } + close $fh; +} + +# Helper function to create an origin node with a test table and a row containing +# the given label. The node is started and ready for use as a source for +# standbys. +sub setup_origin +{ + my ($label) = @_; + my $node = PostgreSQL::Test::Cluster->new($label); + $node->init(allows_streaming => 1); + $node->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $node->start; + $node->safe_psql('postgres', "CREATE TABLE tbl (val text)"); + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); + return $node; +} + +# Helper function to create multiple standby nodes from the same origin node. +# Each standby gets its own backup and data directory, so that they will +# generate independent UUIDs on promotion even though they share the same +# timeline history up to the point of promotion. +sub setup_standbys_from_origin +{ + my ($origin, @names) = @_; + my @standbys; + for my $name (@names) + { + my $standby = PostgreSQL::Test::Cluster->new($name); + $origin->backup($standby->name); + $standby->init_from_backup($origin, $standby->name, + has_streaming => 1); + $standby->append_conf('postgresql.conf', "wal_keep_size = 320MB\n"); + $standby->set_standby_mode(); + $standby->start; + push @standbys, $standby; + } + return @standbys; +} + +# Helper function to wait for multiple standby nodes to catch up to the origin. +sub sync_standbys_with_origin +{ + my ($origin, @standbys) = @_; + $origin->wait_for_catchup($_) for @standbys; +} + +# Helper function to insert a row with the given label into a node's test table. +sub write_record +{ + my ($node, $label) = @_; + $node->safe_psql('postgres', "INSERT INTO tbl VALUES ('$label')"); + $node->safe_psql('postgres', 'CHECKPOINT'); +} + +# Test that pg_rewind detects and handles two standbys that independently +# promoted to the same timeline ID. Before the UUID-based divergence check, +# pg_rewind's same-TLI shortcut would incorrectly skip the rewind in this +# case, leaving the target's diverged WAL intact. +# +# origin (TLI 1) +# | +# +--- node_a (TLI 1) --promote--> TLI 2, UUID-A (target) +# | +# +--- node_b (TLI 1) --promote--> TLI 2, UUID-B (source) +# +# pg_rewind must detect the UUID mismatch and rewind node_a to match node_b. + +my $node_origin = setup_origin('origin'); + +# Create node_a and node_b from separate backups of origin so that each +# has its own data directory and will generate an independent UUID on promotion. +my ($node_a, $node_b) = + setup_standbys_from_origin($node_origin, 'node_a', 'node_b'); + +# Wait for both standbys to catch up to origin, then stop origin. After +# this point the two standbys are isolated and will promote independently. +sync_standbys_with_origin($node_origin, $node_a, $node_b); +$node_origin->stop; + +# Promote both standbys. Each lands on TLI 2 but generates a distinct UUID, +# so the resulting clusters are diverged even though they share a timeline ID. +$node_a->promote; +$node_b->promote; + +# Insert a divergent row on each so the rewind has visible work to do. +write_record($node_a, 'in A'); +write_record($node_b, 'in B'); + +rewind_node($node_a, $node_b, + 'pg_rewind detects independent same-TLI promotions'); + +my $result = + $node_a->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result, "in B\norigin", + 'rewound node has source data, not its own divergent data'); + +$node_a->teardown_node; +$node_b->teardown_node; +$node_origin->teardown_node; + +# Test that pg_rewind correctly rewinds across a TLI mismatch buried in a shared +# prefix of the timeline history. The target has gone through three timelines +# (TLI 1 -> TLI 2 -> TLI 3) while the source independently promoted from TLI 1 +# to what is numerically TLI 2 but with a different UUID (TLI 2'). The deepest +# common ancestor is therefore TLI 1, and pg_rewind must rewind the target all +# the way back to the end of TLI 1. +# +# origin (TLI 1) --+-- node_x --promote--> TLI 2 -- node_a --promote--> TLI 3 +# | (target: TLI 1->TLI 2->TLI 3) +# +-- node_b --promote--> TLI 2' +# (source: TLI 1->TLI 2') +# +# findCommonAncestorTimeline walks forward: TLI 1 entries match (UUID=0 on +# both sides), then TLI 2 vs TLI 2' match on tli and begin but differ on +# UUID, signalling independent promotions. The algorithm therefore backs up +# to TLI 1 as the common ancestor and sets the divergence point to the end +# of TLI 1. + +my $node_origin2 = setup_origin('origin2'); + +# node_x and node_b2 both start from the same TLI 1 baseline. +my ($node_x, $node_b2) = + setup_standbys_from_origin($node_origin2, 'node_x', 'node_b2'); + +# Both standbys must be caught up to the same LSN before origin stops, so +# that TLI 2 and TLI 2' both begin at the same WAL position. +sync_standbys_with_origin($node_origin2, $node_x, $node_b2); +$node_origin2->stop; + +# Promote node_x to TLI 2 (UUID-X) and insert a row. node_b2 is still on +# TLI 1 and has not yet seen any TLI 2 WAL. +$node_x->promote; +write_record($node_x, 'x'); + +# Build node_a2 as a standby of node_x, then promote it to TLI 3. +my ($node_a2) = setup_standbys_from_origin($node_x, 'node_a2'); + +sync_standbys_with_origin($node_x, $node_a2); +$node_x->stop; + +$node_a2->promote; + +# Now promote node_b2 independently from TLI 1 to TLI 2' (UUID-B, != UUID-X). +$node_b2->promote; +write_record($node_b2, 'b'); + +# Rewind node_a2 (TLI 1->TLI 2->TLI 3) from node_b2 (TLI 1->TLI 2') in +# local mode. The rewind must reach back to the end of TLI 1. +# +# node_a2 was initialised from a streaming backup of node_x taken after +# node_x had already completed segment 4 of TLI 2; that segment therefore +# does not appear in node_a2's pg_wal. pg_rewind's backward scan for the +# last checkpoint before the divergence point needs that segment, so we +# point restore_command at node_x's pg_wal and use --restore-target-wal. +# +# Note: no row is inserted on TLI 3. This is intentional: the only +# post-divergence table modification in the target's WAL is the 'x' INSERT +# on TLI 2. On unpatched code the WAL scan would start from the TLI 2 +# shutdown checkpoint (just before TLI 3), miss that earlier insert, and +# leave 'x' in place instead of replacing it with 'b'. +my $node_x_waldir = $node_x->data_dir . "/pg_wal"; +if ($PostgreSQL::Test::Utils::windows_os) +{ + $node_x_waldir =~ s{\\}{\\\\}g; + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'copy "$node_x_waldir\\\\%f" "%p"'\n)); +} +else +{ + $node_a2->append_conf('postgresql.conf', + qq(\nrestore_command = 'cp "$node_x_waldir/%f" "%p"'\n)); +} + +rewind_node($node_a2, $node_b2, + 'pg_rewind rewinds across mismatched TLI 2 / TLI 2-prime to TLI 1', + '--restore-target-wal'); +my $result2 = + $node_a2->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result2, "b\norigin2", + 'rewound node reflects source history, not target TLI 2/TLI 3 data'); + +$node_a2->teardown_node; +$node_b2->teardown_node; +$node_x->teardown_node; +$node_origin2->teardown_node; + +# Test that pg_rewind correctly detects a mismatch when one cluster's TLI 2 +# history entry carries a zero UUID (old-format history file) while the other +# carries a real UUID. The two clusters must have promoted independently, so +# pg_rewind must rewind to TLI 1 rather than accepting the same-TLI shortcut. +# +# Run both orientations: +# (a) target has zero UUID, source has real UUID +# (b) target has real UUID, source has zero UUID +# +# In both cases the setup is: +# +# origin (TLI 1) --+-- node_p --promote--> TLI 2, UUID-P (target) +# | +# +-- node_q --promote--> TLI 2, UUID-Q (source) +# +# One side then has its history file rewritten to the old 3-field format so +# that its UUID reads as zero. pg_rewind must treat zero-vs-nonzero as +# incompatible (they cannot be the same promotion) and rewind to TLI 1. + +for my $strip_target (1, 0) +{ + my $zero_side = $strip_target ? 'target' : 'source'; + my $real_side = $strip_target ? 'source' : 'target'; + my $sfx = $strip_target ? 'zt' : 'zs'; + my $label = + "pg_rewind rewinds when $zero_side has zero UUID and $real_side has real UUID"; + + my $node_origin3 = setup_origin("origin3_$sfx"); + my ($node_p, $node_q) = + setup_standbys_from_origin($node_origin3, "node_p_$sfx", "node_q_$sfx"); + + sync_standbys_with_origin($node_origin3, $node_p, $node_q); + $node_origin3->stop; + + $node_p->promote; + $node_q->promote; + + write_record($node_p, 'in P'); + write_record($node_q, 'in Q'); + + # Strip UUID from the chosen side to simulate a pre-UUID server. + strip_tli_uuid($strip_target ? $node_p : $node_q, 2); + + rewind_node($node_p, $node_q, $label); + my $result3 = + $node_p->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); + is( $result3, + "in Q\norigin3_$sfx", + 'rewound node has source data, not its own divergent row'); + + $node_p->teardown_node; + $node_q->teardown_node; + $node_origin3->teardown_node; +} + +# Test that pg_rewind detects independent promotions to TLI 3 when both +# clusters share a common TLI 1 -> TLI 2 history (same UUID) but independently +# promoted from TLI 2 to TLI 3, producing different TLI 3 UUIDs. +# +# origin (TLI 1) --- node_mid --promote--> TLI 2, UUID-M +# | +# +-- node_c --promote--> TLI 3, UUID-C (target) +# | +# +-- node_d --promote--> TLI 3', UUID-D (source) +# +# The same-TLI shortcut compares entry[Nentries-2].tluuid on each side; that +# is the UUID of the TLI 3 promotion, which differs. The full rewind path +# then walks the history forward: TLI 1 matches (same tli/begin/UUID-M at +# entry[0]), TLI 2 also matches (same tli/begin; UUID-M is the same on both +# sides at entry[0]), but TLI 3 vs TLI 3' differ at entry[1] (UUID-C != UUID-D), +# so the divergence point is set to the end of TLI 2. + +my $node_origin4 = setup_origin('origin4'); +my ($node_mid) = setup_standbys_from_origin($node_origin4, 'node_mid'); + +sync_standbys_with_origin($node_origin4, $node_mid); +$node_origin4->stop; + +# Promote node_mid to TLI 2 and insert a row that both TLI 3 nodes will share. +$node_mid->promote; +write_record($node_mid, 'mid'); + +# node_c and node_d both start as standbys of node_mid so they share the same +# TLI 2 promotion UUID (UUID-M). +my ($node_c, $node_d) = + setup_standbys_from_origin($node_mid, 'node_c', 'node_d'); +sync_standbys_with_origin($node_mid, $node_c, $node_d); +$node_mid->stop; + +# Promote both independently; each generates a distinct TLI 3 UUID. +$node_c->promote; +$node_d->promote; + +write_record($node_c, 'c'); +write_record($node_d, 'd'); + +rewind_node($node_c, $node_d, + 'pg_rewind detects independent TLI 3 / TLI 3-prime promotions sharing TLI 2' +); +my $result4 = + $node_c->safe_psql('postgres', "SELECT val FROM tbl ORDER BY val"); +is($result4, "d\nmid\norigin4", + 'rewound node has source TLI 3-prime data, not its own TLI 3 data'); + +$node_c->teardown_node; +$node_d->teardown_node; +$node_mid->teardown_node; +$node_origin4->teardown_node; + done_testing(); diff --git a/src/bin/pg_rewind/timeline.c b/src/bin/pg_rewind/timeline.c index dda06eaa0bc..b6500606b27 100644 --- a/src/bin/pg_rewind/timeline.c +++ b/src/bin/pg_rewind/timeline.c @@ -9,9 +9,40 @@ */ #include "postgres_fe.h" +#include <ctype.h> +#include <string.h> + #include "access/timeline.h" #include "pg_rewind.h" +/* + * Parse a UUID string in standard dashed form into a pg_uuid_t. + * Returns true on success, false if str is not a valid UUID string. + */ +static bool +rewind_parse_uuid(const char *str, pg_uuid_t *uuid) +{ + const char *src = str; + + for (int i = 0; i < UUID_LEN; i++) + { + char buf[3]; + + if (!isxdigit((unsigned char) src[0]) || + !isxdigit((unsigned char) src[1])) + return false; + buf[0] = src[0]; + buf[1] = src[1]; + buf[2] = '\0'; + uuid->data[i] = (unsigned char) strtoul(buf, NULL, 16); + src += 2; + /* skip dash at positions after bytes 3, 5, 7, 9 (i == 3,5,7,9) */ + if (src[0] == '-' && (i == 3 || i == 5 || i == 7 || i == 9)) + src++; + } + return (*src == '\0'); +} + /* * This is copy-pasted from the backend readTimeLineHistory, modified to * return a malloc'd array and to work without backend functions. @@ -48,6 +79,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) uint32 switchpoint_hi; uint32 switchpoint_lo; int nfields; + char uuid_str[UUID_STR_LEN + 1] = {0}; fline = bufptr; while (*bufptr && *bufptr != '\n') @@ -66,7 +98,8 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) if (*ptr == '\0' || *ptr == '#') continue; - nfields = sscanf(fline, "%u\t%X/%08X", &tli, &switchpoint_hi, &switchpoint_lo); + nfields = sscanf(fline, "%u\t%X/%08X\t%36s", &tli, &switchpoint_hi, + &switchpoint_lo, uuid_str); if (nfields < 1) { @@ -75,7 +108,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) pg_log_error_detail("Expected a numeric timeline ID."); exit(1); } - if (nfields != 3) + if (nfields < 3) { pg_log_error("syntax error in history file: %s", fline); pg_log_error_detail("Expected a write-ahead log switchpoint location."); @@ -99,7 +132,14 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo; prevend = entry->end; - /* we ignore the remainder of each line */ + /* + * Parse the optional UUID field. Old history files have the reason + * string in field 4; its first word is much shorter than UUID_STR_LEN + * so the length check safely distinguishes old from new format. + */ + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); + if (nfields == 4 && strlen(uuid_str) == UUID_STR_LEN) + rewind_parse_uuid(uuid_str, &entry->tluuid); } if (entries && targetTLI <= lasttli) @@ -123,6 +163,7 @@ rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries) entry->tli = targetTLI; entry->begin = prevend; entry->end = InvalidXLogRecPtr; + memset(&entry->tluuid, 0, sizeof(pg_uuid_t)); *nentries = nlines; return entries; diff --git a/src/include/access/timeline.h b/src/include/access/timeline.h index 3aee3419a5c..3b94c4f0a4d 100644 --- a/src/include/access/timeline.h +++ b/src/include/access/timeline.h @@ -13,6 +13,7 @@ #include "access/xlogdefs.h" #include "nodes/pg_list.h" +#include "utils/uuid.h" /* * A list of these structs describes the timeline history of the server. Each @@ -22,9 +23,10 @@ * pointers of all the entries form a contiguous line from beginning of time * to infinity. */ -typedef struct +typedef struct TimeLineHistoryEntry { TimeLineID tli; + pg_uuid_t tluuid; /* from history file; zero if unknown */ XLogRecPtr begin; /* inclusive */ XLogRecPtr end; /* exclusive, InvalidXLogRecPtr means infinity */ } TimeLineHistoryEntry; @@ -33,6 +35,7 @@ extern List *readTimeLineHistory(TimeLineID targetTLI); extern bool existsTimeLineHistory(TimeLineID probeTLI); extern TimeLineID findNewestTimeLine(TimeLineID startTLI); extern void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, + const pg_uuid_t *newTLUUID, XLogRecPtr switchpoint, const char *reason); extern void writeTimeLineHistoryFile(TimeLineID tli, const char *content, size_t size); extern void restoreTimeLineHistoryFiles(TimeLineID begin, TimeLineID end); diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index be718993401..588094090c8 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -22,6 +22,7 @@ #include "access/xlogdefs.h" #include "access/xlogreader.h" #include "datatype/timestamp.h" +#include "utils/uuid.h" #include "lib/stringinfo.h" #include "pgtime.h" #include "storage/block.h" diff --git a/src/include/utils/uuid.h b/src/include/utils/uuid.h index 572d8cf4c36..6839de2e0b2 100644 --- a/src/include/utils/uuid.h +++ b/src/include/utils/uuid.h @@ -17,12 +17,16 @@ /* uuid size in bytes */ #define UUID_LEN 16 +/* length of a UUID string (without null terminator): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx */ +#define UUID_STR_LEN 36 + typedef struct pg_uuid_t { unsigned char data[UUID_LEN]; } pg_uuid_t; -/* fmgr interface macros */ +/* fmgr interface macros (backend only) */ +#ifndef FRONTEND static inline Datum UUIDPGetDatum(const pg_uuid_t *X) { @@ -38,5 +42,9 @@ DatumGetUUIDP(Datum X) } #define PG_GETARG_UUID_P(X) DatumGetUUIDP(PG_GETARG_DATUM(X)) +#endif /* !FRONTEND */ + +extern pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 sub_ms); +extern pg_uuid_t *generate_uuidv7_r(pg_uuid_t *uuid, uint64 unix_ts_ms, uint32 sub_ms); #endif /* UUID_H */ -- 2.53.0 --=-=-=-- ^ permalink raw reply [nested|flat] 330+ messages in thread
end of thread, other threads:[~2026-05-23 14:09 UTC | newest] Thread overview: 330+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-08-30 17:40 [PATCH v20 6/6] Preserve visibility information of the concurrent data changes. Álvaro Herrera <alvherre@kurilemu.de> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net> 2026-05-23 14:09 [PATCH v7] pg_rewind: use UUIDs to detect independent same-TLI promotions Mats Kindahl <mats@kindahl.net>
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